[R] Finding the position of a variable in a data.frame

[Don MacQueen]

You don't need to find out the column index. This works:

    Df[5,'bat'] <- 100

-Don

At 5:01 PM -0400 8/2/06, John Kane wrote:
>Simple problem but I don't see the answer. I'm trying
>to clean up some data
>I have 120 columns in a data.frame.  I have one value
>in a column named "blaw" that I want to change. How do
>I find the coordinates. I can find the row by doing a
>subset on the data.frame but how do I find out here
>"blaw " is in columns without manually counting them
>or converting names(Df) to a list and reading down the
>list.
>
>Simple example
>
>cat <- c( 3,5,6,8,0)
>dog <- c(3,5,3,6, 0)
>rat <- c (5, 5, 4, 9, 0)
>bat <- c( 12, 42, 45, 32, 54)
>
>Df <- data.frame(cbind(cat, dog, rat, bat))
>Df
>subset(Df, bat >= 50)
>
>----results
>   cat dog rat bat
>5   0   0   0  54
>
>
>Thus I know that my target is in row 5 but how do I
>figure out where 'bat' is? 
>
>All I want to do is be able to say
>Df[5,4] <- 100
>
>Is there some way to have function(bat) return the
>column number: some kind of a colnum() function?  I
>had thought that I had found somthing  in
>library(gdata) matchcols but no luck.
>
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-- 
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA